&EPA
                                 United States
                                 Environmental Protection
                                 Agency
                                  Industrial Environmental Research
                                  Laboratory
                                  Cincinnati OH 45268
                                 Research and Development
                                  EPA-600/S2-80-211  Feb. 1981
Project Summary
                                 Process  Spill   Monitoring,
                                 Control  and  Recovery in the
                                 Pulp  and  Paper  Industry

                                 George W. Gove, James J. McKeown,  and Albert J. Carlson
                                   In order to develop strategies to
                                 control intermittent spills associated
                                 with the production of chemical wood
                                 pulp, examinations of process efflu-
                                 ents from kraft pulp mills and investi-
                                 gations  of existing  loss  control
                                 systems were conducted.  Dynamic
                                 computer modelling, using data from
                                 process  effluent  monitoring, was
                                 employed to illustrate the utility of this
                                 technique to arrive at various loss
                                 control  strategies for  particular
                                 process   configurations.  Examples
                                 were presented, using the monitoring
                                 data, of the economic benefit possible
                                 from  recovery  of chemicals and
                                 organic solids. A loss control strategy
                                 for   pulping,  pulp  washing, and
                                 chemical recovery areas was
                                 implemented  in  the existing spill
                                 control system of a large kraft pulp
                                 mill.  Control  was successfully
                                 effected utilizing  a digital computer.
                                 In  addition  to  managing  process
                                 losses, the direct  digital control sys-
                                 tem allowed gathering,  processing
                                 and  managing data obtained from the
                                 sensors monitoring the system.
                                  This Project Summary  was  devel-
                                 oped by EPA's  Industrial  Environ-
                                 mental Research Laboratory.
                                 Cincinnati, OH. to announce key find-
                                 ings of the research project that is fully
                                 documented in a separate report of the
                                 same title (see Project Report ordering
                                 information at back).
                                  Introduction
                                   This report outlines the examination
                                  and characterization of process efflu-
                                  ents and explains a loss control system
                                  for a large kraft pulp mill which utilizes a
                                  digital computer.
                                 Effluent Characterization
                                   Samples were analyzed from process
                                 and liquor storage areas and sewers in
                                 20 pulp  mills -  representing various
                                 locations, ages,  process types,  and
                                 wood species. Because  compositions
                                 varied widely,  predictive  correlation
                                 equations could  not be derived.  The
                                 absolute  values of the  parameters
                                 varied relatively little within each class
                                 of fluid, however, so reasonably consis-
                                 tent  ratios could be established to
                                 describe  different  parameter pairs.
                                 Table 1 gives representative ratios for
                                 weak black liquor (WBL) samples from
                                 the mills tested. As an example, the
                                 data  for  26 different liquor samples
                                 showed  that  biochemical  oxygen
                                 demand (BOD) was approximately 23%
                                 of the total dissolved solids (TS) content,
                                 with a standard deviation of 4%.
                                   Selection of variables for monitoring
                                 was also influenced by the linearity of
                                 the measured response with concentra-
                                 tion. Figure 1 shows how total organic
                                 carbon (TOC) changes in proportion to
                                 weak black liquor  concentration  and
                                 Figure 2 indicates how  conductivity
                                 varies with weak wash concentration.
                                 The data  were obtained by adding con-

-------
Table 1.    Characteristic Parameter Ratios for Weak Black Liquor Samples.
Patio
BOD/TS
TOC/TS
BOD/ TOO
Na/ Conductivity
PCU/ Conductivity
TS/ Conductivity
Average
0.23
0.39
0.59
0.71
4.84
2.90
Standard
Deviation
0.04
0.03
0.08
0.34
1.92
0.84
No. of
Samples
26
28
22
24
34
30
  700
  600
\
 .500-
    H
  400-
^300-
  200-
  700
                           TOC
      Mill Effluent           129
      Weak Black Liquor  55,400
                   TOC= 134 + 511X
                      r2 = 0.999
          0.2   0.4    0.6  0.8   1.0
              WBL - % v/v

Figure 1.    Linearity of TOC response
             weak black liquor added
             to mill effluent.
centrated  samples  incrementally  to
normal mill effluent.
  These findings suggest that pH and
other specific ions, TOC, color, and
conductivity might be appropriate  as
indicators of effluent conditions. pH
was eliminated as lacking the required
sensitivity. Specific ions, TOC, and color
measurements  were  considered  too
expensive for large  monitoring net-
works, in part owing to requirements for
sophisticated sample systems. Conduc-
tivity was found to be a suitable linear
predictor of parameters such as sodium
and TOC; this variable can also serve as
a direct indicator of spills because its
value increases  with dissolved  inor-
ganic solids concentration. Moreover,
conductivity instrumentation is widely
used, relatively  simple, reliable, and
reasonably inexpensive.

Control Equations
, Developing the control equations for
the spill recovery system required that
                                         u
                                        I
                                         I
60


50


40


30


201


70
Lime Mud Weak Wash
      added to
  '   Mill Effluent
                                                        Cond- 1,08 X + 1.33
                                                             r2 = 0.998
                                             0
                                        Figure 2.
   10   20   30
     Weak Wash -
                        40
                        v/v
                                                                         50
      Linearity of conductivity
      response lime mud weak
      wash   added  to  mill
      effluent.
                                        conductivity be related to mass flows of
                                        solids, sodium, and organic carbon from
                                        the  various   processes.  This  was
                                        accomplished using data from process
                                        sewers in pulping, pulp washing, liquor
                                        recovery, and causticizing areas at two
                                        mills. Samples were drawn using auto-
                                        mated equipment at 1 to  12 times per
                                        hour depending on process conditions.
                                        Analyses were made in a laboratory for
                                        accuracy.
                                          Linear equations of the form y-mx + b
                                        were sought, relating conductivity (x) to
                                        other parameters (y). Many  samples
                                        were analyzed and data points like those
                                        in Figure 3 were used with regression
                                        techniques to evaluate slope  (m) and
                                        intercept (b). Table  2 shows values
                                        obtained at the monitoring stations in
                                        one of the mills sampled.
                                        System Design
                                          The loss control system gathers and
                                        analyzes sensor data to detect and log
                                                                                 4000
                                                                                 3000

                                                                                 2000
                                                                                 ;ooo
                                                                                       TOC = 482(cond) - 309
                                                                                       n = 50      r2 = 0.950
      01234567
         Conductivity - mmho/cm

Figure 3.    Linearity of conductivit
             related to TOC.

problems, responds to appropriate siti
ations by queuing remote devices an
notifying  the  operator, and  provide
reports and summaries of occurrences
These functions are implemented usin
a system based on a central compute
with  a keyboard printer for  operate
action and a process input/output (I/C
interface. Sensors include conductivit
flow, and level probes; actuators incluc
pumps, valves, and  samplers.  In tr
system specified, the interface may t
6000 feet from the central processir
unit and the  remote devices can t
1500 feet from the interface.

Operation
  The system was installed in the larg
kraft pulp mill in Figure 4 and include
the monitored stations listed in Table
Sumps receive overflows from varioi
storage  tanks as  well as  leaks fro
transfer pumps and heaters. Each sun
has a conductivity probe, a flow meter,
sampler, and a self-priming pump.
  Effluent normally   flows from tr
batch digesters, brown stock washer
evaporators, and recovery furnaces  '
mill sewers, where flow and conduct!
ity are measured, and then to biologic
treatment. Spills  are picked up by tr
sump  pumps  and  transferred to
200,000-gallon  tank.  The fluid m«
then  be  bled to the  sewer or pump(
back to the 20,000-gallon overflowtai
and into the vats on  the first stages
the washers.
  Ranges of parameters and values
ratios obtained  from the prelimina
analyses were  used  to  determii
conductivity setpoint. Mass flow se
points for Na, TOC, and TS are calc
lated  using flow measurements in tl
equations relating these parameters

-------
Table 2.    Parameters Derived for Use in the Linearized Control Equation (y = mx + b)
Slope
No. of (m)
Station Variable Observations fjmho/cm
1 Na 97 0.249
TOC 50 0.482
TS 59 1.655
2 Na 96 0.308
TOC 68 0.599
TS 33 1.743
3 Na 95 0.261
TOC 55 0.462
TS 40 0.565
4 Na 60 0.258
TOC 40 0.492
TS 42 2.120
SN 7
SN 4 • C
/^~~~\ Spill I
\200K gal\Tank ' > 7 ~ f
\ /S/V 70 I EvapArea |
\s. iX^ r\' f/f\,Af\ /""""""N. A - * ^
->
A f *»i
T \ C^) <
j Recovery ^ lg
1 V/tf"Jace ( ) l^± ) \
' ' 1 i
Overflow* — s.
, v Tan* ^f 20K\
>\9^J
-T-. c«; jr 1 \ ) 1^(*^\
T SN 5 V_V L J
Dump A O'flow
Tank /— v ' f~\ /Recovery
I \--lSBL \ \ c,,rr>ar-a
V 7 V ; \fu»w<.« Loss control
•iguro 4.Schematic of Brown Co., loss control strategy s
Observed Observed
Conductivity Variable Multiple
Intercept Range Range Correlation
(b) /jmhos/cm mg/l Coefficient
-95 702-11730 134-2730 0.951
-309 1 140 - 81 10 144 - 4090 0.950
-884 900 - 18800 440 - 34520 0.943
-87 165 - 9560 18 - 3046 0.995
-101 165-9560 66-5730 0.985
-550 730 - 7160 1860 - 19790 0.977
-81 1166-15300 142-4772 0.974
-363 67-11700 94-5415 0.979
+863 460 - 5800 530 - 6230 0.458
•- 39 238 - 3351 43 - 822 0.988
+ 91 338-9630 249-4950 0.985
-845 350-8200 720-21400 0.928
conductivity. These mass targets rather
— +-To WTP than conductivity are used to initiate
action, so that control is exercised on
Overflow the basis of material being lost, the
~^-Z7\^~^ capacity of the waste treatment plant,
~~t f ) ( ) compatability of new spills with the
* \ J \ ) present contents of the tank, and
A 	 |_ i7i0i ctnrano minimum total solids to be economical-
1_ WBL Oll»oj/c7 ... i.
(j- - „.. j „., j , ly recovered. As an example, high
• 	 L — -. ( J small amount of material is passing
^g"N ' /^T\ ' ^X^ through the system, neither of which
Jj 1  In one instance, a conductivity
1 /^~>\C:i setpoint of 2 mmho/cm at 200 gpm
| \_J corresponded to 484 Ib/day Na, 786
! ^^ Ib/day TOC, and 2700 Ib/day TS. If the
1 V.J SttlpuuUs fot llieac CunSlilumUs weie
O established for reasons of economy or
environmental protection at 900 Ib/day
Na, 4000 Ib/day TOC, and 2900 Ib/day
System TS materja| wou|d not be pumped to
the spill tank unless flow or conductivity
ystem. increased.

-------
Table 3,    Variables Measured at the Monitoring Stations for the Loss Control
            System.
Station
Device 1
Device 2
Device 3   Device 4
Digester Sump
Brown Stock Washer Sump
No. 8 Recovery Sump
Main Kraft Sewer
No. 1 1 Recovery Sump
Caustic/zing Sewer
Total Caustic Sewer
Spill Tank
Spill Tank Valves
Overflow Tank
Weak Black Liquor Tanks
Conductivity
Conductivity
Conductivity
Conductivity
Conductivity
Conductivity
Conductivity
Conductivity
Valve to
Recovery
--
...
Flow
Flow
Flow
Flow
Flow
...
Flow
Level
Valve to
Sewer
Level
Level
Pump
Pump
Pump
...
Pump
...
...
Pump
...
...
...
Sampler
Sampler
Sampler
Sampler
Sampler
Sampler
Sampler
Sampler
...
---
...
Control Strategies
  The sump pumps and the spill tank
valves  may  be  operated  manually,
under analog control using conductivity
setpoints, or  in a direct digital  mode
with  targets   stored  in  computer
memory.  Digital control offers operators
the most immediate and comprehen-
sive information and also offers advan-
tages such as rapid and easy  setpoint
changes.  In  addition,  the  computer
provides  the  best  base  of  data for
management information.
  The  real-time  executive   for  the
computer system has the logic shown in
Figure 5. The program restarts when the
computer is  powered,  and  may  be
initialized at any time for data averag-
ing. The  sensors are read in a burst
every 10 to 15 seconds so all readings
are obtained in the  same relative time
frame.  Each  reading  is converted to
appropriate units, and running averages
are created and stored. Values are
checked to verify whether the sensor is
out of service or if action is already being
taken at the particular station. If not, the
readings  are  compared to parameters
such as low and high limits, allowable
rate of change, a confidence period to
determine if a condition has been out of
tolerance too long, and the number of
               | Start Program ]
             No
                   Initialize
                   Program
                  Batch Read
                   Sensors
                  Check One
                Sensor Reading
                Reading Within
                  Set Points?
  All Readings
    Checked?
                 Perform Data
                   Analysis
                 Store Results
                  In Memory
                  I  Real Time  ,
                No'  Appications '
                     Program  |
                  •   Modules  i
              Free Computer for
              Off Line Programs
            Figure  5.    Real  time  executive
                        program module.
times  the  system  must   detect  £
condition out of tolerance during the
confidence interval. If readings are no
within  the  setpoints, control  is
transferred to a real-time application:
module like that in Figure 6, comprising
routines for each  station and sensoi
which activate  pumps or  valves  am
notify the operator of situations  anc
actions taken.
Enter From
Executive
*
Confidence
Interval
Exceeded?
No

Problem
Exist?
Yes

Initiate
Action
                                                                                                   /   Print
                                                                                                   (   Inform
                                                                                                    \ Operator t
                                                                                                           -—
                                                    Figure 6.
                                                  On  line  applicatio,
                                                  module general structurt
                           The  executive  and   application
                         modules run in the foreground mod<
                         The executive completes a cycle in les
                         than 5 ms if no action is required, and i
                         about 500 ms if control is transferred t
                         the applications  modules  for  ever
                         station.  Since the sensors  are rea
                         every 10 s, time is available to run othc
                         programs  in  the  background.   Fc
                         example,  the  operator  ma
                         communicate with the system throug
                         the printer to monitor selected sensor
                         change tolerance  parameters  c
                         setpoints,  open or close  valves, tur
                         pumps on  or off, activate  samplers, <
                         mark sensors or control devices in <
                         out of service for maintenance.

                         Performance
                           The loss control strategy has bee
                         monitoring, intercepting and recoverir
                         process spills and losses in the pulpin
                         pulp  washing and chemical recove
                         areas of a  large kraft pulp mill for ov<
                         two years.  During that time all materi

-------
that has been sent to the spill tank has
been returned to the chemical recovery
system, which has resulted in the spill
tank being generally less than 20% full.
Because  of this,  the spill tank also
served as extra weak black liquor stor-
age, but only during times of high liquor
inventory,  as during mill shutdowns or
when evaporators were  out of service.
During a  representative  18-day period
the system  intercepted  and returned
nearly 900,000 gallons containing more
than 12 tons of sodium, 15 tons of BOD
and 67 tons of dissolved solids.
                                           George W. Gove. James J. McKeown, and Albert J. Carlson are with the North-
                                             east Regional Center, Department of Civil Engineering, Tufts University,
                                             Medford, MA 02155.
                                           D. L.  Wilson is the EPA Project Officer (see below).
                                           The complete report, entitled "Process Spill Monitoring, Control and Recovery in
                                             the Pulp and Paper Industry," (Order No.  PB 81-131  971; Cost: $17.00,
                                             subject to change) will be available only from:
                                                   National Technical Information Service
                                                   5285 Port Royal Road
                                                   Springfield. VA22161
                                                   Telephone:  703-487-4650
                                           The EPA Project Officer can be contacted at:
                                                   Industrial Environmental Research  Laboratory
                                                   U.S. Environmental Protection Agency
                                                   Cincinnati, OH 45268

-------
United States                           Center for Environmental Research                                                Fees'paid"
Environmental Protection                  Information                                                                  Environmental
Agency                                C.ncinnati OH 45268                                                          Protection
                                                                                                                 Agency
                                                                                                                 EPA 335


Official Business
Penalty for Private Use $300

                                    ST
          CHICAGO  IL  60604

-------